Effect of curing temperature on surface and subsurface properties of polyurethane elastomer

Polyurethane elastomers are a class of polymers with two-phase segmented structure. The study of their features at the microstructure level will make it possible to control both macroscopic physical and mechanical properties of polymers and functional properties of surfaces. Polyurethanes of the same formulation were synthesized in this work, varying the curing temperature from 30 to 90 degrees C. Atomic force microscopy, dynamic mechanical analysis, and wettability were used in the study. Stiff fibrillar supramolecular structures (elastic modulus 14-22 MPa), distributed in a softer matrix, are formed in the polymers. Phase inhomogeneities are hidden under the surface by a soft nanolayer of variable thickness. An increase in the curing temperature leads to an increase in the thickness of this layer, and the stiff structure transforms from homogeneous to a network of agglomerates. Wettability, free surface energy and macroscopic viscoelastic properties nonlinearly depend on the curing temperature, which is explained by the physical and mechanical properties of the stiff and soft phases.